Algal biorefinery culminating multiple value-added products: recent advances, emerging trends, opportunities, and challenges

Abstract

Algal biorefinery is rising as a prominent solution to economically fulfill the escalating global requirement for nutrition, feed, fuel, and medicines. In recent years, scientific productiveness associated with microalgae-based studies has elaborated in multiplied aspects, while translation to the commercial level continues to be missing. The present microalgal biorefinery has a challenge in long-term viability due to escalated market price of algal-mediated biofuels and bioproducts. Advancements are required in a few aspects like improvement in algae processing, energy investment, and cost analysis of microalgae biorefinery. Therefore, it is essential to recognize the modern work by understanding the knowledge gaps and hotspots driving business scale up. The microalgae biorefinery integrated with energy-based products, bioactive and green compounds, focusing on a circular bioeconomy, is urgently needed. A detailed investigation of techno-economic analysis (TEA) and life cycle assessment (LCA) is important to increase the market value of algal products. This review discusses the valorization of algal biomass for the value-added application that holds a sustainable approach and cost-competitive algal biorefinery. The current industries, policies, technology transfer trends, challenges, and future economic outlook are discussed. This study is an overview through scientometric investigation attempt to describe the research development contributing to this rising field.

Introduction

Algae-based biofuel is the perceived solution, especially for problems like global warming, pollution, and high energy demand in developing countries. The terrestrial plants fix 3–6% CO₂ per annum, whereas around 40% CO₂ is fixed by microalgae, macroalgae, cyanobacteria, and seagrass (Fabris et al. 2020; Ansari et al. 2019). Algae are putative source of inexhaustible fuel that can replace fossil fuels. Nevertheless, algae fuel production is not yet economically viable, hence, attention is being diverted towards algal biorefinery concept. Algal biorefinery has numerous environmental benefits like CO₂ fixation, wastewater treatment, along with industrial applications like the production of biofuel, biomethane, biohydrogen, biodiesel, bioethanol, carbohydrates, lipids, pigments, proteins, and biochar (Dolganyuk et al. 2020; Özçimen et al. 2015). Algal biomass is used as food supplements and animal feed because of enhanced proteins and lipids (Singh et al. 2020; Barros et al. 2015). The biorefinery approach comprises distinct steps: cultivation, harvesting, cell disruption, extraction, purification, efficient assessment, and related policies (Kannah et al. 2021). Extensive examination is required on each step to attain efficient and sustainable algae biorefinery approach. Algal biorefinery is an integrated circular bioeconomical approach that encourages zero waste management with self-sustainability; hence, it can be considered a green-based technology (Vasistha et al. 2021a, b).

LCA and TEA are significant aspects to be discussed in algal biorefinery that include assessing CO₂ emission, cost analysis, and energy consumption in biofuel production (Yadav et al. 2019; Mälkki and Alanne 2017). The crucial parameters, including technology advancement, economic efficacy, environmental sustainability, policy framework, and industrial awareness, need to be focused on making microalgae value-added products commercially viable.

In literature, various studies discussed microalgae biorefinery pathways, distinct software for LCA and TEA evaluation, production of value-added bio-products. Saral et al. (2022) reported the different pathways of algae biorefinery with their economic and environmental investigation by LCA and TEA, however, did not discuss the impact of pathways on market policies and technology transfer (Saral et al. 2022). Banu et al. 2020 majorly focuses on algal biorefinery frameworks, market analysis and LCA but significance of value-added products and TEA is lacking. Kannah et al. (2021) elucidated the biochemical conversion of algal biorefinery with other aspects such as LCA, TEA, and value-added products but commercialization and current market trends were not discussed (Kannah et al. 2021). Microalgae biorefinery based on bioremediation are widely elaborated by Sharma et al. (2022), however, the commercialization of value-added products in the various industrial sector and challenges of microalgae biorefinery from wastewater were missing (Sharma et al. 2022). In contrast, our review majorly emphasizes economic and environmental sustainability, current research progress, and market analysis in the algal biorefinery field contrary to previous research reporting majorly on processing and environmental aspects of biorefinery. This review focuses on the significance of (i) integrated approach of algae biorefinery (ii) self-sustainability and environmental feasibility (iii) valorization of algae biomass to obtain value-added products (iv) TEA and LCA for opting suitable strategies (v) the technology transfer trends, and government policies implemented for regulating framework of biofuel market.

Outlook of algal biorefinery

There are specific acknowledged strategies for cultivation, biomass recovery, and extraction of value-added products from distinct algal species. The three foremost modes of algae cultivation are photoautotrophic, heterotrophic, mixotrophic, and photohetrotrophic (Vasistha et al. 2021a). However, large-scale algae cultivation in open ponds, raceways, tubular photobioreactors, and flat plate photobioreactors are reported (Daneshvar et al. 2021). Various known harvesting techniques for algal biomass recovery include manual centrifugation, flocculation, filtration, and floatation. Subsequently, different extraction processes, including chemical, mechanical, physical, and enzymatic, are applied to harvested algae biomass to acquire tremendous value-added products (Yadav and Rai 2022). Certain prevalent extraction techniques are transesterification, hydrothermal treatment, cracking, ultrasonic-assisted extraction, electroporation, isotonic extraction, and so on Banerjee et al. (2022).

Algae biorefinery is considered a sustainable bioeconomic strategy to valorize biomass for industrial applications. Simultaneously producing bioenergy and other value-added co-products such as polyunsaturated fatty acids (PUFA), pigments, antioxidants, and protein meal are imperative for offsetting the high production cost of algal biofuels (Mohan et al. 2020; Arora et al. 2021). Due to environmental benefits, algal biorefinery-based biofuel and value-added products are leading the industry. Oleaginous algal biomass is essential to produce biofuels such as biodiesel and other value-added products like PUFA and nutraceuticals (Chen and Lee 2019). The remaining de-oiled algal biomass is a prominent source of carbohydrates, proteins, amino acids, pigments, and nutrients (Fan et al. 2020). Various processing methods have been explored to treat de-oiled algal biomass based on prerequisite biomass standards, processing state, and process outcome (Chen and Lee 2019). In a study, Scenedesmus Bijugatus grown in a 250 L vertical tubular photobioreactor yielded 0.26 g/L per day (dry weight) biomass with 63 mg/L per day lipid, which was utilized to generate 0.21 g biodiesel and 0.158 g ethanol. Here, Scenedesmus Bijugatus demonstrated biodiesel production and ethanol biosynthesis to reduce the overall expense of the process (Kumar et al. 2019). In another approach, the de-oiled algal biomass or lipid extracted algal hydrochar (LEH) is further gasified in supercritical water to extract gaseous fuels within the biorefinery. In Nannochloropsis sp., biomass slurry was hydrothermally carbonized (HTC) to acquire hydrochar, with nutrients and small organic compounds from the aqueous phase, recycled for algal growth. Later, supercritical water gasification (SCWG) of LEH was performed at 600 °C for 6 h, resulting in 75% energy recovery and absolute retrieval of nitrogen in the form of ammonia (Lu and Savage 2015).

The minimization of external energy needs, water, and nutrient demands might be achieved by utilizing a biorefinery approach, with energy and material symbiosis between unit functions. The integral production of biodiesel, biogas, and bioethanol from algal biorefinery helps to upgrade the cost-effectiveness of bioenergy generation (Singh et al. 2020; Martínez-Gutiérrez 2018). The strategy of utilizing by-products of biodiesel extraction and purification process, combined with different processes and waste materials, is considered as a closed-loop approach (Gue et al. 2018). Algae biorefinery is one such closed-loop approach with high economic and environmental sustainability, as mentioned in Fig. 1. A significant reduction in the overall cost of the process was observed when biodiesel and other products like bioethanol, butanol, biochar, biogas, carbohydrate, proteins, pigments, antioxidants, polyunsaturated fatty acids (PUFA), and monounsaturated fatty acids (MUFA) are also produced.

Fig. 1.

Schematic representation of algal biorefinery closed-loop approach (Mohan et al. 2020; Banu et al. 2020)

In biodiesel production, glycerol is an additional product considered a beneficial growth substrate for culturing oleaginous microalgae. Various industries accept glycerol as a feed and improved fuel additive (Gue et al. 2018). In pharmaceutical and cosmeceutical industries, colouring agents, nourishments, and fragrances are produced by pigments and carotenoids (Pierobon et al. 2018). Global demand for algal carotenoids is increasing rapidly, mainly for lutein, astaxanthin, and total carotenoids are considered 358 million USD in 2024, 814 million USD in 2022, and 1.53 billion, respectively (Kumar et al. 2020a, b, c; Carotenoids market by type 2021; Astaxanthin market by source, 2022). The residual algal biomass left after biodiesel and value-added products extraction is utilized as fertilizers and bioplastic feedstock in the agricultural and bioplastic industry (De Corato et al. 2018). The closed-loop approach makes the algae-mediated biorefinery environment friendly and beneficial from a business perspective. Another benefit of the closed-loop strategy is the circular economy depicted by LCA and TEA analysis of algae-mediated biofuel production (Liu et al. 2019). Comparing biodiesel production from microalgae and jatropha in a circular loop approach, the material circularity indicator (MCI) scores high for algae biodiesel (Gue et al. 2018). MCI scores in the above study are based on circularity level, GHG emission, and indirect product extraction. This approach encourages zero waste management, recycling, and reutilizing by-products as raw material for the next algae cycle, making it a self-sustainable concept (Hemalatha et al. 2019). GHG balance of bioenergy generation may get disorganized because of fossil fuel at various stages of the biomass supply chain. Nevertheless, it can be sustained by reducing fossil energy utilization by alternatively enhancing waste CO₂ and nutrient-laden water streams (Yadav et al. 2020).

According to LCA, the algal biomass production and drying processes are highly energy-intensive processes considering the comprehensive energy requirement of 54.98% (Taelman et al. 2015). A LCA-oriented study was conducted on Nannochloropsis sp. under 24 different conditions based on cultivation, harvesting, and lipid extraction techniques. The study reveals that algal biodiesel GHG balance can be enhanced using nutrients from waste and CO₂ (Monari et al. 2016). An innovative and tenable concept of the algal biorefinery is the integration of heterotrophically grown algae using wastewater for its remediation and the proper valorization of de-oiled biomass (Mohan et al. 2015). Encouraging wastewater utilization in heterotrophically grown algal biomass with appropriate lipid valorization in a closed-loop approach presents novel scope (Choudhary et al. 2020). Astals et al. demonstrated anaerobic co-digestion of algal biomass from Scenedesmus sp. with pig manure to produce biogas, proteins, and lipids. In the study, lipid and protein were extracted from Scenedesmus sp. The biomass remnant was digested with pig manure, leading to 29–37% methane yield (Astals et al. 2015).

Co-production of algal ethanol and biodiesel is an appropriate process where dilute acid pre-treatment leads to sequential segregation of lipid and ethanol by distillation and solvent extraction, respectively (Laurens et al. 2015). An Integral approach toward processing algal slurry decreases the expense of algal biofuels like fatty acid methyl esters (FAMEs) and ethanol together by 9%, which also leads to a reduced energy outcome of 476.96 LGE t -1 biomass at $2.84 per L Gasoline Equivalent (LGE) (Kumar et al. 2019). In an integral biorefinery approach, β-carotene, ω-3 fatty acids, biodiesel, glycerol, and bioethanol were extracted from mixotrophically grown Scenedesmus obliquus through a sequential protocol, which resulted in 0.06 g of β-carotene, 2 g of ω-3 fatty acids, 38 g of biodiesel, 3 g of glycerol and 17 g of bioethanol. Hence, generating various value-added products from individual feedstock in an integral algal biorefinery approach makes the process sustainable and cost-effective.

Comparing the collaborative production of biodiesel, biohydrogen, and biobutanol to individual production concerning the processing and maintenance cost, the collaborative approach was seen as economically more prominent. The algal bioenergy generation depends on the cost of biomass feedstock (Ahorsu et al. 2018). Various stress-based research shows enhanced yield of biodiesel and value-added products, making the algal biorefinery approach a more prominent alternative to fossil fuel. In a study, eight integral microalgae biorefinery frameworks carrying fresh water and marine algae grown in nitrogen-depleted conditions for GHG balance, energy consumption and eutrophication potential were studied (Kaur et al. 2021; Cheng et al. 2022). Their effect was examined on biomolecular components, which revealed enhanced lipid accumulation under nitrogen-depleted conditions (Brownbridge et al. 2014). Marine algal species recycle most nutrients under nitrogen depletion, while freshwater species cannot. As a result, marine species contribute less to eutrophication than freshwater (Brownbridge et al. 2014). Carbohydrates, proteins, and lipids from wet algae biomass can be converted into biodiesel, bioethanol, and alcohols, while the de-oiled biomass is a source of monomeric sugars such as glucose, galactose, and mannose, used to synthesize biohydrogen, alcohol, and bioplastics (Khanra et al. 2020a, b; Trivedi et al. 2015). Three different methods for algal bio-oil production were compared in a study that concludes that the slow pyrolysis of remaining algal biomass after lipid extraction is beneficial over the slow pyrolysis of fresh dry microalgal biomass (Silva et al. 2016a, b). Technical advancement and further research are essential to upgrade the sustainability and beneficial aspect of the algal biorefinery strategies for biofuel utilization instead of fossil fuel.

Plethora of algal value-added products

Algae as a promising source of fuel

Biodiesel

Microalgae can incorporate CO₂ during algae photosynthesis and convert it into useable molecules for biodiesel production. Hence, the CO₂ liberated during combustion gets utilized, leading to carbon–neutral fuel. Due to this environment-friendly quality of algal fuel is considered a highly productive and sustainable energy feedstock (Yaşar 2020). Successful integration of wastewater technology with algae biomass production provides different fatty acids used for biodiesel production (Sun et al. 2018). Removal of intracellular lipid is necessary for obtaining biodiesel from microalgae, and the process needs to be energy-efficient for economic biodiesel production (Sajid et al. 2016). Some process gives rise to low-quality biodiesel, such as micro-emulsification, pyrolysis, and catalytic cracking. The process of transesterification is prominently used to convert algal oil to biodiesel, where the Triacyl glycerides (TAGs) react with alcohol in the presence of acid or base catalyst to give fatty acid alkyl esters (FAMEs). In the transesterification process, unrefined oil reacts with alcohol in the presence of a catalyst resulting in fatty acid methyl ester and glycerol as by-products. In microalgae, raw and viscous lipids (TAGs, free fatty acids) are transformed into low molecular weight fatty acid alkyl esters (Santos-Sánchez et al. 2016). There are different catalysts used during the transesterification process (a) alkaline catalysts like potassium hydroxide, sodium hydroxide, and sodium methoxide, (b) acid catalysts like hydrochloric acid, sulfuric acid, and sulfonic acid phosphoric acid, (c) enzymatic catalyst like lipases and (d) inorganic heterogeneous catalyst like solid phase catalyst. The industries consider acid catalysts favorable, but alkaline catalysts are 400 times more efficient (Tang et al. 2020a, b). Algal species mainly studied for biodiesel production are Chlorella vulgaris and Chlorella protothecoides because of their excellent biomass and relatively high oil content (de Morais et al. 2015). The factors that influence the transesterification process are the molar ratio of alcohol to oil, type of alcohol, type and amount of catalysts, reaction time, temperature, and purity of reactants. The most suitable conditions for maximum biodiesel production are a 9:1 methanol/oil molar ratio 1.5% KOH catalyst/oil ratio for 10 min (Tang et al. 2020a, b; Zappi et al. 2019).

The lipase enzyme used in enzymatic transesterification is of two kinds: intracellular and extracellular (Santos-Sánchez et al. 2016). Lipase being a biocatalyst for the transformation of biodiesel from algae under moderate conditions with comparatively easy downstream processing for biodiesel and by-products segregation makes this a lucrative option. However, one of the crucial complications with enzymatic transesterification is the high cost of lipase, enzyme inactivation in the presence of methanol with glycerol, and the slow rate of reaction, compared to the conventional method. FAME profiling of the algae-based biodiesel revealed the biodiesel standards and characteristics such as Cetane Number (CN), Iodine Value (IV), Cloud Point (CP), and Cold Filter Plugging Point (CFPP) that matches the standards set by the International Biodiesel Standard for Vehicles (Rizwan et al. 2018). These standards consider various factors, including fuel properties, oil content impact on the engine, and emission properties (Mofijur et al. 2022).

Biogas

Biogas is an inexhaustible fuel that comprises mainly CO₂ and methane (CH₄) and some other gases. The quality of biogas depends mainly on the relative amount of methane, which depends on the substrate and fermentation conditions. Biogas production comprises four major processes: hydrolysis, acetogenesis, acidogenesis, and methanogenesis (Pan et al. 2019). In the case of microalgae, the higher lipid and protein content makes it less than the ideal feedstock for biogas through anaerobic digestion. However, microalgae can utilize the CO₂ emanating from the biogas stream and increase the methane content of the biogas, thereby improving its fuel properties. Gasification is one more method to generate biogas that includes partial oxidation and a combustible gas mixture of biomass at high temperatures (Santos-Sánchez et al. 2016; Situmorang et al. 2020).

Bioethanol

The microalgal polysaccharides are broken down into simple sugars using suitable microorganisms, and bioethanol can be synthesized from various microalgae. Comprehensive carbohydrates are naturally found in algae, e.g., starch, cellulose, laminarin, mannitol, and agar. Cholorococcum, Chlamydomonas, and Chlorella are a few species known for synthesizing bioethanol for their greater conversion rate than other algal species (de Morais et al. 2019; Asimakopoulos et al. 2018). Chlorococcum sp. produces ethanol under dark conditions and has 27% starch that can be utilized in 24 h at 25˚C, making it a prominent bioethanol source (Banerjee et al. 2022). Various green algae species include Dunaliella, Chlorella, Chlamydomonas, Arthrospira, Sargassum, Spirulina, Gracilaria, Prymnesium parvum, Euglena gracilis, and Scenedesmus are known for bioethanol production (Sun et al. 2018). Bioethanol production is also carried out using the seaweed Ulva lactua by yeast fermentation. Plackett–Burman's experimental design based on the immobilization technique on supported solid materials is an optimized method for bioethanol production (El-Sayed et al. 2016). This experiment reveals that bioethanol production is affected by various factors such as sugar concentration, pH level, and the size of the inoculums.

High carbohydrate content and ease in cultivation make the brown algae suitable feedstock for ethanol production by fermentation. Brown seaweeds such as Ascophyllum nodosum and Laminaria digitata can produce bioethanol by biomass pre-treatment and hydrolysis through dilute sulphuric acid as well as certain commercially available enzymes (Tedesco et al. 2021). Fermentation of Laminaria hyperborean by the yeast Pichia angophora produces a high amount of ethanol from laminarin and mannitol (Obata et al. 2016). From dry algal biomass, 49% sugar was obtained on acid pre-treatment while 20% was studied on enzymatic hydrolysis (de Souza et al. 2020). The yield of ethanol synthesis by seaweed after fermentation is usually 0.08 and 0.12 kg/kg dry seaweed. It depends on different pre-treatment and hydrolysis processes and algae genera (Gao et al. 2020). In the case of Ulva lactuca, ethanol production after hydrothermal pre-treatment declined even after removing sugar. Fermentation using acid hydrolysis agar for the conversion of sugar into ethanol reported in red algae is low.

Bio-jet fuel

Globally, the airline industry requires 5 million barrels of oil per day. CO₂, water vapor (H₂O), nitrogen oxides (NOx), carbon monoxide (CO), sulphur oxides (SOx), unburned or partially combusted hydrocarbons, particulates, and other trace compounds produced during jet fuel combustion are hazardous to the environment (O'Neil et al. 2019).

These airline industries change the world's atmosphere resulting in climate change and ozone depletion (Parker 2021). The main focus of the airline industry is to reduce its carbon footprint by using eco-friendly fuel. Bio-jet fuel is renewable fuel in the aviation industry that can decline 60–80% airlines related greenhouse gas emissions compared to fossil fuel-oriented jet fuel (Datta et al. 2019). Jet fuel is classified as civil or commercial jet fuel and military fuel. Commercial jet fuel is further classified into three subcategories: Jet A-1, Jet A, and Jet B, among which JetA-1 and Jet A are kinds of kerosene fuels, but Jet B is the combination of gasoline and majorly kerosene so that it can be utilized in frosty climate. Military jet fuel is classified as JP-4, JP-5, and JP-8. Antioxidants, dispersants, and corrosion inhibitor properties make JP-5 and JP-8 chemically intensified to fulfil the needs of the aviation sector (Kumar et al. 2019).

To obtain distinct properties required by the aviation industry, the bio-jet fuel is made using a mixture of microalgae biofuel and regular petroleum jet fuel, which is termed green bio-jet fuel (Why et al. 2019). Algal biomass is converted into liquefied hydrocarbon fuel through gasification mediated by synthetic gas production, particularly CO and H₂, and by Fischer–Tropsch (F–T) process (Chen et al. 2015). By hydrotreatment (hydrotreated fatty acids and esters, HEFA), the microalgae biodiesel can be transformed into jet fuel as certified by ASTM standard D7566. The fuel obtained can be utilized as a commercial mixture with at least 50% conventional jet fuel. Therefore, this type of fuel is called Hydrotreated Vegetable Oil (HVO), Hydrotreated Renewable Jet (HRJ), or Bio-derived Synthetic Paraffinic Kerosene (Bio-SPK). Synthesis of Bio-SPK/HEFA includes oil cleaning by eliminating the impurities through a specific method. Removing oxygen results in short-chain diesel-range paraffin, converting olefins to paraffin through hydrogen mediated process. The elimination of oxygen and removal of olefins leads to enhancement in the heat of combustion and thermal and oxidative stability. The subsequent reactions are isomerization and crack diesel range paraffin to attain jet range carbon numbers resulting in the synthesis of a similar molecule in regular petroleum jet fuel (Goh et al. 2022).

Various aviation industries are conducting worldwide research and practical implementations of microalgae biofuel. Flight Continental 737–800 was tested for 1.5 h on 7th January 2009, fueled with a 50:50 mixture of bio-jet fuel produced from 47.5% jatropha, 2.5% algae, and Jet-A1 fuel. Another attempt was made with flight JAL 747–300 of 1.5 h on 30th January 2009, fueled with a 50:50 mixture of bio-jet fuel obtained from feedstock camelina 84%, jatropha 16%, and algae 1% (Hendricks et al. 2011).

Biohydrogen

The forthcoming desire for clean fuel can be overcome by generating biohydrogen from algae. Despite a few challenges of biomass pre-treatment, conversion efficacy, extensive storage, and economic viability algae is a most eminent source of biohydrogen production (Mandotra et al. 2021). The enormous industrial attention is attained by algae-mediated biohydrogen production, the three major ways known for biohydrogen production are water photolysis, acidogenic stage of organic matter anaerobic digestion, and dual-stage dark fermentation (González-Fernádez et al. 2012). Algae rises as a prominent source of biohydrogen production due to the ability of photolysis of water molecule into hydrogen via hydrogenase activity. Algae species like Chlamydomonas reinhardtii and Anabaena variabilis have obtained extra interest due to their immensely higher enhanced hydrogen production capacity (De Bhowmick et al. 2019). Biohydrogen synthesis on a massive scale is not industrially viable due to excessive manufacturing cost, involvement of modern machinery, utilization of extremely sensitive hydrogenase enzyme, and reduced biomass fixation. The major challenge with algae-mediated photolysis is the oversensitivity of hydrogenase enzymes toward oxygen. To evade this challenge of photosynthetic inhibition to produce H₂ and O₂ are momentarily alienated among dual stages. In usually photosynthesis H₂ abundant substrate is used to secure CO₂ followed in stage I followed by nurturing of microalgae under the sulphur deprived condition in stage II. Various research suggested that under aerobic and sulphur deprived conditions the algae cell wall carbohydrate is converted into hydrogen and ultimately leads to biohydrogen production (Bhattacharya and Goswami 2020). H₂ production from algae by photolysis is highly energy efficient in contrary to water electrolysis (Show et al. 2018). Hence, for CO₂ consumption as an air contaminant and sustainable water use for biohydrogen production, algae-mediated biophotolysis is the most prominent strategy. However, to conquer the challenge of low productivity from algae at a commercial scale innovative advancements in techniques are immensely required. Genetically modified microalgae and co-culture with other microbes might be another solution for H₂ yield enhancement.

Algal bioactive and nutraceutical compounds

Lipids

Microalgae are evaluated as a suitable source for biofuel synthesis based on their fatty acid profiles, similar to soya oil with respect to the degree of the carbon–carbon bond (Yaşar 2020). Under specific conditions, microalgae biomass constitutes about 50% triglycerides (TAG); out of which about 70% are unsaturated and that is an appropriate form of lipid for biodiesel production (Sun et al. 2018). In microalgae, palmitic acid (C16:0), palmitoleic acid (C16:1), stearic acid (C18:0), oleic acid (C18:1), linoleic acid (C18:2), and linolenic acid (C18:3) are normal triglycerides, and the rest of the lipids are mostly diglycerides and phospholipids. Polar lipids such as MUFA, PUFA, waxes, glycolipids, or phytosterols, and non-polar lipids like TAG molecules are synthesized by microalgae in large amounts (Santos-Sánchez et al. 2016). Fatty acid alkyl ether, green diesel, and bio-oils are the algae-derived biodiesel, as shown in Fig. 2. About 70% of the unsaturated lipid content of the algae-derived biodiesel leads to reduced cold flow problems, whereas in phospholipids, the elevation of phosphate groups leads to increased cat-cracking units (Tang et al. 2020a, b).

Fig. 2.

Algal biorefinery towards multiple product generation (Özçimen et al. 2015)

PUFA such as docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), linoleic acid (LA), gamma-linolenic acid (GLA), and arachidonic acid (AA) are synthesized in massive amounts by certain microalgae (de Morais et al. 2015). Algae-derived PUFA manifests numerous properties such as antioxidant, antibacterial, antiviral, detoxification, hypercholesterolemia prohibition, enhancing brain potential, and boosting immune-stimulatory effects (de Morais et al. 2015). DHA oil from algae, marketed by Martek Bioscience, is a supplement for an infant which is validated by Food and Drug Administration (FDA). Schizochytrium sp. and Crypthecodinium cohnii are reported to produce abundant DHA. The PUFA, DHA, and EPA from microalgae are the ultimate source of omega-3 fatty acids, with a cost of around $80–160 kg⁻¹ and potentially reaching around $898.7 million by 2025 (Tang et al. 2020a, b). Fish was considered the primary source for DHA production a couple of years back but is found unsuitable due to drawbacks like the foul smell and prohibition of fish oil as a food ingredient by vegans (Bartek et al. 2021). Also, a global decrease in fish stock was observed due to leakage of ship fuel and toxic industrial waste containing mercury, dioxins, chlorinated pesticides, and polychlorinated biphenyls (PCB) (Zappi et al. 2019). In contrast to seed oil, the microalgae lipid has a higher amount of omega-3 fatty acid, which makes microalgae lipid production economically sustainable (Rizwan et al. 2018; Benavente-Valdés et al. 2016).

Pigments

Algae are photosynthetic organisms with various light-sensitive pigments with distinct functions. Besides chlorophyll, there are photosynthetic compounds like phycobiliproteins and carotenoids. Microalgae are gaining enormous attention as a natural source of pigments and carotenoids. These pigments are utilized in various nutraceutical, pharmaceutical, and cosmeceutical industries, as manifested in Table 1. Because of health and environmental safety considerations, synthetic products like pigments are a significant defeat. In such circumstances, microalgae pigments and carotenoids such as β-carotene, astaxanthin, canthaxanthin, and phycobiliproteins have been recognized as a great relief (Shourie et al. 2022). Pigments are utilized as natural colorants in orange juice, chewing gum, ice sorbets, candies, soft drinks, dairy items, and edible supplements (Sun et al. 2015). Pigments and carotenoids prevent various diseases like cancer, metabolic disorders, diabetes, eye diseases, and neurogenerative disorders. Pigments are highly utilized as diagnostic tools like fluorescent markers (O'Neil et al. 2019).

Table 1.

Major compounds extracted from algae for industrial applications

Compounds	Algae species	Bioactivity	Industry involved	Uses	References
Pigments  Chlorophyll a  Chlorophyll b  Canthaxanthin  Lutein  Lycopene  Astaxanthin  β carotene  Phycobilin  Phycocyanin  Fucoxanthin	Aphanizomenon flos-aquae Chlorella sorokiniana Chlorella zofingiensis Chlorella vulgaris Dunaliella tertiolecta Dunaliella salina Haematococcus pluvialis Artrhospira platensis Spirulina platensis	Antioxidants, UV ray protection, bioavailability, food colorant, animal feed, enhance immune functions, improve eye/skin health, anti-aging property, antiviral, anti-diabetes, anti-obesity, anticancer, anti-inflammatory, anti-allergic, anti-osteoporotic	Pharmaceutical, cosmeceutical and nutraceutical	Food additive, cosmetic component, medicinal compound	Lasta et al. (2022); Shourie et al. (2022); Liu et al. (2021); Novoveská et al, (2019)
Lipids  Hydrocarbon  Triacylgycerols  PUFAs- DHA, EPA, ARA, GAL, MUFAs	Botroycoccus braunii Cyanophora paradoxa Chlorella vulgari Glaucocystis nostochinearum Nannochloropsis salina Neochlorisoleoabundan Nannochloropsissalins Phaeodactylumtricornutum Rhodomona salina Scenedesmu sp. Schizochytriummangrovei Khawkineaquartana Palmodictyonvarium Parietochloris incise Rhabdomonas incurve	Provide energy, Infant brain development, increase immunity, antidepressant, anti-inflammatory, anticancer, antioxidant, anti-tumor, treating rheumatological disease, treating kidney disease, treating hypertriglyceridemia	Bioenergy industry, pharmaceutical and nutraceutical industry	Biofuels, food and feed additives	Konur (2021); Xue et al. (2021); Villarruel-López et al. (2017)
Proteins  Leucine  Asparagine  Glutamine  Cysteine  Arginine  Aspartate  Alanine Glycine Lysine Valine Phycobiliproteins Lectins	Chlorella ellipsoidea Chlorella vulgaris Euglena gracilis Nannochloropsis oculata Porphyridium cruentum Rhodomonas salina Scenedesmus sp. Spirulina platensis	Built and repair muscles, anti-hypertension, renal protective, ant-hyperlipidaemia, immunostimulant, antiviral activities, antibacterial, anti-nociceptive, anti-inflammatory, platelet aggregation inhibition, and anti-adhesion, s anti-oxidative, anti-tumour, neuroprotective, and hepatoprotective activity	Pharmaceutical and nutraceutical industry	Nutritional supplements, food and feed additive	Ho and Redan (2021); Strauch and do Nascimento Coutinho (2021); Koutra et al. (2018)
Carbohydrates  b1–3 glucan  Amylose  Starch  Cellulose  Alginates  Laminaran	Isochrysis galbana Porphyridium cruentum Spirogyra sp.	Provide energy, Anti-coagulants, Anti-rheumatic, Anti-influenza Anti-epileptic Neuroprotective Anti-angiogenic/anti-metastatic, Anticoagulant, Anti-angiogenesis, anti-tumour, Anti-cancer	Bioenergy industry, pharmaceutical and nutraceutical industry	Biofuels and medicinal applications	Lasta et al. (2022); Chowdhury et al. (2019); Mu et al. (2019)

The antioxidant characteristic of carotenoids lacking in synthetic colorants is developing a significant role in pharmaceutical and cosmeceutical industries, as shown in Table 2 (Sathasivam et al. 2018). Astaxanthin is considered a "super oxidant" due to its high antioxidant activity in comparison to other carotenoids (Sarma et al. 2021). Astaxanthin is a keto-pigment with various anti-inflammatory, anti-apoptotic, and singlet molecular oxygen-quenching activity (Cao et al. 2021). In contrast to tocopherol, astaxanthin has 100-fold more health benefits due to its antioxidant property (Sztretye et al. 2019). Haematococcus pluvialis naturally produces astaxanthin under stressed conditions, when the thin flagellated algae cell turns red non-motile cell (Telli and Şahin 2020). A Few microalgae species considered major astaxanthin producers are Haematococcus pluvialis, Chlorella zofingiensis, Chlamydomonas nivalis, Botryococcusbraunii, Chlorella Vulgaris, Monoraphidium sp., Chlamydocapsa sp., Neospongiococcum sp., Chlorococcum sp. and Scenedesmus obliquus (Cao et al. 2021). Astaxanthin has been commercially produced from Haematococcus pluvialis by Alga Technologies Ltd., Asta Real Inc., Beijing Gingko Group (BGG), Cyanotech Corporation and Parry's Pharmaceuticals (Tang et al. 2020a, b).

Table 2.

Versatile potential of algal carotenoids in various industries

Carotenoid	Species	Yield	Cost	International Market Value	Bioactivity	Industrial Applications	Companies	Reference
β-carotene	Dunaliella salina, Posidonia oceanica, Cymodocea nodosa	27 mg/g	300-3000USD/Kg	618.94 million USD by 2026	Antioxidant, antiproliferative, anti-inflammatory	Food and beverage colorant, food and feed additive, antioxidant agent, Immune stimulating, anti-aging, cancer and cardiovascular diseases preventive	Aqua Carotene (USA), Cognis Nutrition & Health (Australia), Cyanotech (USA), Nikken Sohonsha Corporation (Japan), Tianjin Lantai Biotechnology (China), Parry Nutraceuticals (India), Seambiotic (Israel), Muradel (Australia)	Bekirogullari et al. (2020); Harvey and Ben-Amotz (2020)
Leutine	Dunaliella salina, Chlorella sp, Scenedesmus almeriensis Posidonia oceanica, Cymodocea nodosa	31.4 mg/L	500USD/Kg	454.8 million USD by 2026	Cardiovascular protective, ADM prevention, Cardiovascular protective, Anti-inflammatory, Antioxidant, Antiproliferative,anti-obesity	Pharmaceuticals, dietary supplement, pet food, fish feed	Orcas International, Inc. (USA), A Clover Nutrition (China), Reindeer Biotech (China), Ambe (India), Dynais (France), YBS Corporation (Japan), Aaco Vege-tech Company (China)	Galasso et al. (2017)
Astaxanthin	Haematococcus pluvialis	23.2 mg/g	6000USD/Kg	800 million USD by 2026	Antioxidant, Antiproliferative, immune system stimulation, anti-obesity, Cardiovascular protective	Animal feed colorant, nutraceuticals, pharmaceuticals, cosmetics	Alga Technologies (Israel), Cyanotech (USA), Jingzhou Natural Astaxanthin Inc. (China), Algaetech International (Malaysia), Parry Nutraceuticals (India), Mera Pharmaceuticals Inc. (USA), Fuji Chemicals (Sweden)	Bhattacharya and Goswami (2020), Niizawa et al. (2018)
Fucoxanthin	Sargassum siliquastrum, Hijikia fusiformis, Undaria pinnatifida, Laminaria japonica, Alaria crassifolia, Cladosiphon okamuranus	18.3 mg/g	168.62USD/Kg	600 million USD by 2025	Antiproliferative, Antioxidant, UV protection, anti-obesity	Nutraceuticals, cosmeceuticals, pharmaceuticals	AlgaNova International (China), Leili Natural Products Co., Ltd. (China)	Nagi et al. (2021)

β-carotene (retinol) is a precursor, which gets converted into vitamin A in the human body. Vitamin A displays diverse advantages in the health sector like cornea protection, anti-aging, anticancer, immune modulation, prevent cardiovascular diseases, and requisite for expecting mothers and children (Situmorang et al. 2020). Anti-carcinogenic property has also been observed in β-carotene, according to National Cancer Institute. In treating cardiac diseases, β-carotene was used to influence cholesterol levels. The significance of Vitamin A can be estimated by the health issue generated by its deficiency, including immune impairment, night blindness, xerophthalmia, and blindness in children. In contrast to synthetic β-carotene, microalgae extracted β-carotene is more efficient antioxidant with improved properties. Synthetic β-carotene produces only trans-isomers; instead, the algal β-carotene produces either cis or trans-isomers. β-carotene is also being utilized as additives in animal feed and food colorant (Mata et al. 2010). Dunaliella salina, Dunaliella tertiolecta, Dunaliella bardawil, Botryococcus braunii, Chlamydomonas nivalis, Chlamydomonas acidophila, Chlorococcum sp., Chlamydocapsa sp.,Tetraselmis sp. and Chlorella sorokiniana are few of the microalgae species known for β-carotene production (Barkia et al. 2019; Sathasivam et al. 2019).

Microalgae carotenoid lutein is utilized to treat age-related macular degeneration, prevent cardiovascular diseases, cataracts, and certain kinds of cancers, based on its excellent antioxidant property (Sun et al. 2015). Chlorella sp., Botryococcus braunii, Dunaliella tertiolecta, Chlamydomonas nivalis, Scenedesmus almeriensis, Pyrgocythara urceolata, Coelastrum proboscideum, Chlamydomonas acidophila, Neospongiococcum gelatinous, Chlamydocapsa sp., Muriellopsis sp., Pyramimonas sp. and Tetraselmis sp. are some microalgae species for lutein production (O'Neil et al. 2019).

Biomolecules

Microalgae are considered a significant feedstock for protein and carbohydrate production, for example, Chlorella Vulgaris for glycoproteins, Spirulina platensis for C-phycocyanin, and Porphyridium cruentum (Orfanoudaki et al. 2020). Chlorella sorokiniana, Cocculinella minutissima, Chlorella luteoviridis, Albuca spiralis, Chlamydomonas nivalis, Aphanizomenonflos-aquae, Scenedesmus sp. and Stichococcus sp. are the microalgae species exploited for the production of amino, as these can absorb strong UV radiations (Orfanoudaki et al. 2020; Sathasivam et al. 2018). Spirulina contains 60% raw protein with vitamins, minerals, and biologically functional compounds that are consequently utilized as food supplements in aquaculture and poultry industries (Bhattacharjee 2016). Algal proteins have also been extensively explored as biofertilizers, commercial enzymes, bioplastics, and even surfactants. Some reported enzymes synthesized from microalgae for commercial purposes are phytases, α-galactosidase, protease, laccases, lipase, cellulases, amylolytic enzymes, antioxidant enzymes, and carbonic anhydrase (Brasil et al. 2017). According to their spectral properties, phycobiliproteins are widely distributed into three vital groups: Phycocyanin, allophycocyanin, and phycoerythrin (Freitas et al. 2022). In the nutraceutical and cosmeceutical industries, Phycocyanin and Phycoerythrin obtained from algae are essential, as shown in Table 1. Phycobiliproteins have distinctly fluorescent characteristics, due to which it is used as a labeling reagent in various techniques, including flow cytometry, fluorescence immunoassay, immunohistochemistry, and other biomedical science activities (Chew et al. 2017; Manirafasha et al. 2016). For a natural blue pigment c-Phycocyanin, Spirulina platensis is considered as the putative source (Chew et al. 2019). The manufacturers and suppliers of phycobiliproteins are Biotech Corp, Columbia Bioscience, and Quanta Phy. Inc (Hu 2019).

In red algae, vital polysaccharides are found carrageenan and agar, while in brown algae, glucan, mannitol, and alginate are the important carbohydrates observed (Khanra et al. 2020a, b). Alginate (alginic acid) is the main component of the cell wall in brown algae that comprises of about 40% dry weight (Baweja et al. 2016). In a food, cosmetics, stabilizers, emulsifiers, lubricants, thickening agents, and clinical drugs, the algal carbohydrates are utilized by various industries. Other microalgal polysaccharides can act as metal ion chelators and bind to micronutrients important for plant nutrition (Michalak and Chojnacka 2015). Types of polysaccharides ulvans, carrageenan and fucoidans are known as sulphate polysaccharides as these contain sulphate esters (da Silva Vaz et al. 2016a). These exhibit anti-tumor, antiviral and antioxidant properties and are also explored as food additives and are usually obtained from Chlorella Vulgaris and Scenedesmus quadricauda. Sulphated polysaccharide is also known to obstruct the migration and adhesion of polymorphonuclear leukocytes due to which it is used in curing anti-inflammatory skin disorders. A cosmeceutical product marketed as Alguronic acid is a mixture of polysaccharides extracted from green algae (Malik et al. 2020).

Green products

Biochar

The solid, carbonized product acquired after the thermal decomposition of algae biomass under limited oxygen supply is known as biochar. Biochar obtained from microalgae consists of aggregates within the 10–100 μm with a 1 μm irregular porosity (Das et al. 2018). The microalgal biochar has a lower carbon content surface area and cation exchange capacity than the lignocellulosic biochar. It has higher pH and hence can be used to balance acidified soil. It is rich in nutrients like nitrogen, ash and inorganic elements, adding to soil fertility. It is also applied to the soil to protect it from undesirable microorganisms (Michalak and Chojnacka 2015). It is widely used for air and water cleansing because of its hydrophobic and absorbent properties, along with functional groups having hydrophilic nature like carboxylic acids, aldehyde, and hydroxyl (Mohan et al. 2020). Accordingly, biochar is used as a strengthening agent in cement and organic polymers, a carbon source for synthetic gas synthesis and a substitute for coke in steel production due to its low ash content (Michalak and Chojnacka 2015).

Bioplastics

Biopolymer produced from microalgae is most acceptable globally in contrast to synthetic polymers. Recent research shows upgraded mechanical properties in algae-mediated biopolymers compared to synthetic polymers (Beckstrom et al. 2020). Biodegradable characteristics of algae-mediated bioplastic are a cause of global attention. Polyhydroxyalkanoates (PHAs) are one of the algae-based biodegradable plastic polymers which can be classified into three categories based on the number of carbon atoms in the backbone of biopolymers a short chain with ≤ 5 carbon, a moderate chain with 6 ≤ 14 carbon, and long-chain ≥ 15 carbon (Raza et al. 2018). Various PHA-originated products like Biopol, Nodax, Degr Pol, and Biogreen are present in the market for different applications (Dietrich et al. 2017; Anjum et al. 2016). Algae protein can generate bioplastic via a thermo-mechanical polymerization reaction (Devadas et al. 2021). Utilizing microalgae for the production of bioplastic is much more prominent and economical due to the presence of high protein content (Khalis 2018). Chlorella sp. and Spirulina sp. due to their high and complex protein content, are successfully utilized for bioplastic production polymers (Devadas et al. 2021; Chia et al. 2020).

Green nanoparticle

A new and green approach for synthesizing nanoparticles is using algae mainly belonging to Phaeophyceae, Chlorophyceae, and Rhodophyceae (Chugh et al. 2021). As discussed above, algae is an affluent source of secondary metabolites and various biomolecules, leading to considerable nano-biofactories (Nahvi et al. 2021). Algae exhibit various benefits including metal hyper-accumulation, fast doubling time, convenient handling, non-toxic, cost-effective, and environmentally suitable for the biosynthesis of green nanoparticles (Negi and Singh 2018). Hence, algae are prevalent for synthesizing distinct metallic and metal oxide nanoparticles such as silver, zinc, gold, palladium, etc. (Chaudhary et al. 2021). The green synthesis of nanoparticles is influenced by various physical parameters including pH, type of metal, metal precursor concentration, bio extract, reaction mixture intact duration, light source, temperature, and so on (AlNadhari et al. 2021). The size, shape, and crystallinity of the nanoparticles directly depend upon the nucleation, growth, aging, agglomeration, and stabilization of nanoparticles influenced by the above-mentioned physical parameters (Aboelfetoh et al. 2017). Algae-mediated nanoparticles attain global attention considering versatile biomedical applications like gene therapy, anticancer therapy, drug delivery, antimicrobial activity, biosensors, and imaging (Mandhata et al. 2022).

Exopolymers (EPS)

Microalgae EPS have been emerged as the sustainable alternative for various biotechnological process. Environmental biotechnology has pioneered the use of these biopolymers as biosurfactants and heavy metal biosorbents (Babiak and Krzemińska 2021). These are ways for reducing pollution that are both economically and environmentally effective. EPS are carbon and energy reserves for cells that are frequently expelled by microalgae as part of physiological processes or when they are under stressed (Moreria et al. 2022). During physiological activities, microalgae produce large amounts of EPS compounds, notably at the decline of the growth phase, when the extracellular polymer acts as a flocculant. In a study, the auto flocculation activity in presence of EPS was studied for Scenedesmus obliquus AS-6–1 until the end of the exponential phase, which increased with cultivation period and medium cell concentration (Guo et al. 2013). Additionally, EPS are also necessary for the formation of a biological soil crust (biofilm). By causing surface sealing and pore blockage, this treatment decreases water infiltration into the soil. As a result, the availability of nutrients increases, and the aggregate stability of the soil improves. The microalgae Chlorella minutissima, Chlorella sorokiniana, and Botryococcus braunii were studied for EPS synthesis (Moreria et al. 2022). The effects of nitrogen and carbon contents in the culture media, as well as light intensity, on EPS formation were investigated Koçer et al. (2021). Bhati and Mallick et al. (2015) observed P and N deficiency results in P(3HB) accumulation in Nostoc muscorum while studying the thermal and mechanical properties of P(3HB) and P(3HB-CO-3HV) copolymer films obtained by microorganism. EPS also has antioxidant, anti-inflammatory, anticancer, antiviral, antibacterial, and immunomodulatory properties, all of which help to advance natural medicines and nutraceuticals industry.

Techno-economic feasibility

Algae-based biofuel is a futuristic approach in the world's energy scenario, but besides algae-based investigations and technological development, the most vital aspect of analyzing for the commercialization of algae products is the expense of processes employed. Simultaneous synthesis of value-added products during algae fuel production is the most cost-effective and feasible method to decrease manufacturing cost. Kuppens et al. (2015) delineate TEA as an evaluation of economic feasibility of a new technology that aims to improve the social or environmental impact, and that helps the decision makers in directing research and development or investments. The TEA model creates comprehensive analysis of direct connection among economic and technical aspects of algal biorefinery approach (Thomassen et al. 2018).

The total manufacturing cost is obtained by summing the direct and indirect production costs and general manufacturing expenditure. Net present value (NPV), Return on investment (ROI), Discounted payback period (DPP) and Internal rate of return (IRR) are four economic indicators, which helps to evaluate the project investment as represented in Fig. 3.

Fig. 3.

The major economic indicators of TEA in algal biorefinery (Wu and Chang 2019)

The NPV is usually determined using following equation (Wu and Chang 2019).

$$\text{NPV}=\sum _{t=0}^{\mathit{Nt}}\frac{C\left(F\right|t}{{\left(1+r\right)}^t}.$$ 1

Referring the Eq. 1, cumulative discount price $CF\left|t\right)is$ estimated by applying following equation, where TCI is total capital investment and TMC is total manufacturing cost (Wu and Chang 2019).

$$CF\left|t\right)=\left(\sum _i^m{Y}_{\text{fuel}}^i\times P_{\text{fuel}}^i+\sum _j^n{Y}_{\text{Prod}}^j\times P_{\text{Prod}}^i\right)\left|t-\text{TCI}\left|t-\text{TMC}\left|t\right)\right)\right).$$ 2

DPP is a deviation of reimbursement period evaluates the time required to recover the original funding costs, additionally money owed for the time assessment of the project. NPV and DPP are directly influenced by $CF\left|t\right)$ (Turton et al. 2008).

The IRR obtained through an equation mentioned below (Wu and Chang 2019).

$$0\sum _{t=0}^{\mathit{Nt}}\frac{\text{CF}\left|t\right)}{{\left(1+\text{IRR}\right)}^t}$$ 3

TEA model can be prepared in Excel, nevertheless inputs from precise process design software, including Aspen Plus (USA), DESIGN II (USA), ChemCad (USA), SuperPro Designer(USA) and UniSim Design(Canada) are considered relevant (Shah et al. 2016a, b; Kasani et al. 2022).

In the microalgae cultivation system, external factors, including temperature, intensity of light, and nutrient availability, affect algal species, creating variation in product profiles (Singh and Patidar 2021). Consequently, highly controlled, and optimized conditions are required to attain the desirable products. Lipid elevation leads to depletion of value-added products in biomass, which influences the economy. The major complications in the economic evaluation are CO₂ supply costs along with unpredictable behaviour of downstream processing. The open pond cultivation system is preferred over photobioreactors (PBRs) as it is four times less expensive. Kumar et al. (2020a, b, c) reported TEA of microalgae biomass cultivated on dairy wastewater, examined via capital expenditure (CAPEX) and operational expenditure (OPEX) analysis. They reported remediation of ~ 240,000 m³ of wastewater at cost of ~ $0.482 kg⁻¹ with 504 tons/yr of microalgal biomass production. Large volume V-shaped pond is preferred as reduced land foot printing and cost. Remediation of commercial waste directly by microalgae leads to 80% treated water suitable for agricultural practices (Kumar et al. 2020a, b, c). The equation used to determine microalgae biomass production price (MBPP) in ($/kg) is mentioned below:

$$\text{MBPP}\left(\mathrm{\$}/\text{Kg}\right)=\frac{\text{CRF}\times \text{CAPEX}+\text{OPEX}}{\text{TBM}},$$ 4

where CRF is Capital recovery factor estimated by percentage of interest rate and project lifespan. The model was developed with Aspen Plus software.

Algae-mediated biofuel production can become inexpensive only when suitable options are opted such as Dunaliella salina cultivated in an open pond system instead of PBRs to produce β-carotene nonetheless Haematococcus pluvialis cultivated in PBRs can be used to extract astaxanthin, which has a high market value of about $ 1200–1500. TEA model in above study was created by excel based spreadsheet model (Thomassen et al. 2016). Table 3 displays functioning large-scale algae cultivation for extraction of biofuel and value-added products at commercial level by distinct companies.

Table 3.

Large-scale production of algal products produced by distinct companies profitably

Company/suppliers	Country	Item	Cultivation system	Profit	References
Alga technologies	Israel	Astaxanthin	Closed and semi-closed bioreactors under high light intensity	$ 7.7 million	Shah et al. (2016a, b)
Sapphire energy Inc	United states	High value oils, aquaculture and animal feed	Open pond, photosynthetic growth system	$37.6 million	Banu et al. (2020)
Bio Real Inc	United states	Astaxanthin	Indoor photobioreactor	$49.46 million	Shah et al. (2016a, b)
Cyanotech	Hawaii	Astaxanthin, Spirulina pacifica as food ingredient	Raceway pond and photobioreactors	$ 21.23 million	Panis and Carreon (2016)
Algenol Biotech LLC	United states	Bioethanol, gasoline, jet fuel, biodiesel	Photobioreactor	$ 3.1 million	Algenol Biotech (2019)
Algae. Tec	Australia	Biofuel, animal feed, animal feed, aquaculture feed	Photobioreactor	$ 93 K	Algenol Biotech (2019)

Nevertheless, low biomass production and excessive water requirement increase the cost of the entire process (Malik et al. 2020; Vasistha et al. 2021b; Davis et al. 2014). Harvesting the microalgae biomass from both raceway ponds and PBRs is costly due to expensive dewatering process. Fasaei et al. (2018) performed the TEA on microalgae harvesting and dewatering in both open and closed systems using TEA model generated by excel. The operational expense of harvesting and dewatering in open and closed system were observed 0.5–2 €·kg⁻¹ and 0.1–0.6 €·kg⁻¹ algae biomass, respectively, with the energy requirement of 0.2–5 kWh·kg⁻¹ of algae for open system and 0.1–0.7 kWh·kg⁻¹ algae for closed system. Hence, they concluded that harvesting and dewatering contribute 3–15% of the production costs of algae biomass, which can be reduced by opting appropriate cultivation system and harvesting techniques. Flocculation of the microalgae culture is preferred over centrifugation for biomass harvesting on account of low energy consumption and cost (Fasaei et al. 2018).

Lipid content enhancement in algal biomass makes the algal biofuel more economically sustainable (Togarcheti et al. 2017). Usually, 30% lipid is achieved from approximately10,000 tonnes of algae feedstock at the cost of $2.80/L, and with petroleum, the cost is about $1.10/L, the process configuration is modelled using Aspen Plus (Banu et al. 2020; Davis et al. 2011). Few species like Nannochloris sp., Dunaliella sp. and Chlorella sp. are able to produce 50% lipid content (Harvey and Ben-Amotz, 2020). Based on fatty acid profiling, it can be inferred that algal oil has a high amount of saturated fatty acids (SFAs) and polyunsaturated fatty acids (PUFAs). Cold flow and oxidative stress properties deteriorate simultaneously due to the high amounts of SFAs and PUFAs. Algal biodiesel has also been approved on the limit of kinematic viscosity decided by standards (Thomassen et al. 2016). The algae biorefinery module for TEA was developed by using GREET model for large-scale algal cultivation and biofuel production by downstream processing. It was evaluated that with a minimum market cost of $5 /Gal to $22 /Gal; the capital needed for biodiesel synthesis is approximately$9.8–20.5/Gal (Pérez-López et al. 2018). The cost of biodiesel increases due to high energy consumption during anaerobic digestion in the form of heat (approximately 2.5 MJ/ kg DM) and electricity (approximately 0.39 MJ/ kg DM) (Wang et al. 2020). TEA conducted on biorefinery model to sequester CO₂ from upstream coal-fired power plants and recycles the CO₂ produced for algae cultivation to obtain value-added products. It became discovered that the optimum CO₂ sequestration and usage value turned into reduced from $33.65/ton of CO₂ to $9.52/ton of CO₂ as the power plant length of 300–2400 MW. This study involves MINPL optimized model proposed to reduce CO₂ sequestration along with TEA constraints (Gong and You, 2014) Methane production range from 0.16 to 0.80 CH₄/kg DM depends upon the composition of algal species and biodegradable potential (Barlow et al. 2016). About 40–50% of the capital of entire manufacturing is consumed during downstream processing, which is based on the item manufactured. Techno-economic feasibility of the integrated biorefinery approach is estimated as $14.16 million total investment, $17.42 million internal return rate, 3.3 years reimbursement duration with $8.19 million total existing value. The result leads to the co-production of various products, including biodiesel, glycerol, biogas, and animal feed, making this approach highly feasible (Kumar et al. 2019).

Microalgae cultivation on wastewater and processing of that biomass thermo-chemically by hydrothermal liquefaction (HTL) make the production of biodiesel techno-economically viable and environmentally friendly (Rahbari et al. 2021). Microalgae have the potential to grow on wastewater together with waste streams that reduce the cost of artificial media and remediate the wastewater. It contains nutrients such as nitrogen (majorly ammoniacal nitrogen), carbon (both organic and inorganic), and phosphorus, thereby reducing the cost of the growth medium. Water under its threshold level has high energy, reducing energy consumption up to 60–80% in tertiary treatment (Persiani et al. 2021).

Naturally occurring algae carrying lipids or modified algal cells from direct photosynthetic transformation makes the whole process more economical by reducing downstream processing expense (Banu et al. 2020). The price of algal processing to get biogas and biodiesel can be decreased via upgrading, mainly primary and secondary harvesting methods. After lipid extraction, the de-oiled microalgae biomass was demonstrated to digest anaerobically, making this approach cost-effective and eco-friendly (Vargas-Estrada et al. 2021).

Algal biodiesel is considered a viable option for future transport energy as the energy intensity of algal biodiesel is 2.5 times exceeding that of conventional diesel (Lim et al. 2021). Algal biodiesel production can become economical and environmentally sustainable by its co-production and electric decarbonization during production (Santos-Sánchez et al. 2016). This approach becomes more feasible by producing biodiesel from lipid and synthesizing bioethanol enzymatically from the remaining de-oiled algae biomass (Kouzuma and Watanabe 2015).

Based on ongoing algal fuel research, many small-scale companies have already established a problem related to techniques and methods. For the commercialization of algal fuel, genetic alteration of algae species with an advance downstream approach for separation and extraction is significantly required. Mainly, upstream improvement regarding genetic alteration of algal species and downstream improvement for segregation and extraction technologies are mandatory. The integrated biorefinery approach is the only option to make algal fuel economical and catch the interest of various industries to its profitability and environmental sustainability, as shown in Fig. 4 (Dasan et al. 2019).

Fig. 4.

Algal biorefinery a circular sustainable approach (De Bhowmick et al. 2019)

Hence, in a precise way to make algal biodiesel economical, following aspects are required to be considered including increasing (a) photosynthetic potential and production, (b) advancement in cultivation system, reduced requirement of water and nutrient, (c) modified cell harvesting techniques, (d) suitable lipid extraction and cell disruption methods (e) increase the simultaneous synthesis of high value-added products (f) decrease biodiesel manufacturing expense from algal lipid (g) attention on zero waste management.

Life cycle assessment (LCA)

LCA analysis is a comprehensive evaluation of the effect of any algal product on the environment, viability, and energy dynamics. As determined by guidelines of international organization for standardization (ISO) with series 14040/44 to conduct LCA four major segments are defining goal and scope, life cycle inventory (LCI) analysis, life cycle impact assessment (LCIA) and life cycle interpretation (Talwar and Holden 2022). Steps evaluated in LCA are algae cultivation, dewatering, extraction, conversion, and production of biodiesel and value-added products (Strazza et al. 2015). Various biofuel production techniques and economic feasibility have been successfully evaluated through LCA (Olguín et al. 2015). LCA measures the sustainability and environmental effects of the algae-based biofuel processes (Chowdhury and Franchetti 2017). Net energy ratios (NERs) and greenhouse gas emissions (GHG) are evaluated using LCA. Comprehensive energy efficacy of algal biorefinery is estimated in terms of NER. A biorefinery approach considered economically viable when energy investment remains less than energy obtained therefore NER < 1 indicated cost-effective biorefinery approach (De Bhowmick et al. 2019). The equation for calculating NER is given below (John et al. 2011):

$$\text{Net Energy Ratio}=\frac{\text{Energy obtained}}{\text{Energy invested}}$$ 5

From an industrialization perspective, different cultivation, harvesting, and extraction techniques were analysed in Table 4. The GHG ratio was found to be excessive in the case of de-oiled algal biomass (Kyriakopoulou et al. 2015).

Table 4.

LCA based study on variety of algae species undergoing biorefinery approach and their environmental effects

Algae	Industrial products	Environmental effects	Economical analysis	References
Arthrospira platensis	Food and animal feed	Non-renewable energy consumption, GWP, respiratory inorganics emissions	Autotrophic and heterotrophic cultivation provides a better yield than the traditional method	Olguín et al. (2015)
Chlorella sp.	Biodiesel, protein, bioethanol and succinic acid	CO2 emission, GWP, FER, water footprint	High energy is required in cultivation, dewatering and lipid extraction in addition to CO2 emission, but bioethanol, biodiesel, protein and succinic acid are obtained Overall generating biofuel is not economically viable	Kyriakopoulou et al. (2015)
Dunaliella salina	β-carotene and fertilizer	ADP, GWP, ODP, H-toxicity, ACP, EP, POP, E-toxicity MAEP, FWAEP	High energy is required for harvesting, cultivation, pumping and dewatering, but UAE method mediated high pigment yield give an economic benefit	Quinn and Davis (2015)
Nannochloris sp. and Nannochloropsis sp.	Biodiesel and biogas	GWP, PM10, PM2.5, NOx, and Sox. POP, non-renewable energy consumption	GHG emission and high energy demand in the cultivation process but to reduce cost and GHG emission wastewater is utilized	Monari et al. (2016), Pacheco et al. (2015)
Scenedesmus dimorphus	Biodiesel	GHG emission	Nitrogen-deficient cultivation increase biodiesel yield and decrease GHG emission, but less output energy is obtained than input energy	Monari et al. (2016)
Spirogyra sp.	Biohydrogen and pigments	GHG emission	High energy required for harvesting, pigment extraction and fermentation heating lead to CO2 emission Less pigment yield obtained in comparison to cost Cost is reduced by using electrocoagulation and the solar drying process	Posada et al. (2016)
Tetraselmischui	Bio oil, Biogas, Biochar and Biodiesel	GWP, ADP, Land transformation and use, Water resource depletion, EP, ACP, E-toxicity, H-toxicity, Photochemical smog, OD, Ionising radiation, Respiratory effects	High energy required in cultivation, drying and pyrolysis process	Banu et al. (2020)

GWP global warming potential; FER fossil energy requirement; ADP abiotic depletion; EP eutrophication potential; E-toxicity ecotoxicity; H-toxicity: human toxicity; OD ozone depletion; POP photochemical oxidation potential; ACP acidification potential; MAEP marine aquatic ecotoxicity potential; FWAEP fresh water aquatic ecotoxicity potential; UAE ultrasound-assisted extraction

To enhance the feasibility of the algal biorefinery process, optimization of growth conditions, advancement in techniques along with the utilization of co-products are essential. Prominently, environmental effects of a process are analysed in LCA specifically, based on conventional and integrated methods for biofuel production (Kyriakopoulou et al. 2015). SimaPro software analyses GHG emissions of the whole biorefinery process. LCA model obtained using GREET Model 2013 for bioenergy production from microalgae conducted through HTL with NER 1.23 and − 11.4 g CO₂-eq (MJ)⁻¹ GHG emission contrary to bioenergy production via pyrolysis with NER 2.27 and 210 g CO₂-eq (MJ)⁻¹ GHG emission Bennion et al. (2015). Banu et al. (2020) reported a comparative research analysis of conventional and integrated biofuel production technology on environment using SimaPro software. The result revealed that 94% GHG emission was observed in conventional extraction with 84% energy consumption instead 50% GHG emission was reported in microalgae integrated approach. Mu et al. (2014) use the GREET model to perform LCA on 16 distinct pathways, among which they reported the most environmentally sustainable pathway is algal cultivation followed by wet lipid extraction with − 6.9 kg of CO₂ eq kg⁻¹ GHG emissions (Mu et al. 2014). In a study performed by Sun et al. (2019), LCA model generated by software of OpenLCA was applied in algae-mediated biofuel production. Study aimed at evaluation of LCA of transesterification, HTL, pyrolysis, anaerobic digestion deprived of pre-treatment and anaerobic digestion with pre-treatment, the NER values obtained are1.52, 1.25, 2.46, 1.27 and 0.71, respectively, along with − 10.37, − 6.77, 265.26, − 173.02 and − 60.84 g CO₂ − eq GHG emission. Among these techniques, the most economical and eco-friendly approach was anaerobic digestion with pre-treatment (Sun et al. 2019). Consideration of raw matter and any discharges during synthesis, aqueous, aerial or land, are also included. The algal biodiesel shows low impacts for eutrophication and land use, which is explained by the high biomass yield and use of wastelands. Also, algae biofuel has less impacted soil acidification and human toxicity because of the lack of fertilizer and pesticides usage (Banu et al. 2020).

Industries and technology transfer analysis

Recently, numerous industries and research organizations have been involved in microalgae biorefinery to establish a remarkable global market. A few companies, Solazyme, Zen U Biotechnology Co. Ltd, Cyanotech Corporation, and Algaeon Inc, are actively marketing valuable products obtained from microalgae (Silva et al. 2020). Euglena Co. Ltd, based in Japan, founded in 2005, has developed defatted Euglena biomass for the rich protein source (Ritala et al. 2017). Euglena Co. Ltd and Algaeon are selling β glucan from Euglena. Cyanotech Corporation is the producer of Spirulina used as a food ingredient; the company is based in the US a reached a total revenue of 32 billion in 2016. Some microalgae species like Dunaliella salina and Aphanizomenon flosaquae are marketed by Qianqiu Biotechnology Co. Ltd for β carotene and Blue-green food for β glucan, respectively. Vigani et al. mentioned the company's survey for the product formation from microalgae biomass, which can be utilized as feed or food (Vigani et al. 2015). The worldwide microalgae pigment astaxanthin market has recently reached USD 600 million in 2018 and is expected to reach USD 800 million in 2025 (Global Market Insights 2019). The primary company involved in the commercial production of astaxanthin was Asta Real group, established in 1994. Astaxanthin is marketed in three different varieties Asta Real oleoresin, Asta Real EL25, Asta Real 1010 (Silva et al. 2020). The increasing market interest in Phycocyanin pigment has reached the global market value of USD 112.3 in 2018. The French company algosource (www.algosource.com) develops liquid Phycocyanin, whereas another company named Sipra produces power phycocyanin can be explored for health benefits. The company Sun Chlorella (www.sunchlorella.com), based in the United Kingdom, manufacture Chlorella powder, granules, and tablets prepared by mixing Chlorella extract with malic. The European organization has funded project ABACUS (Horizon 2020) on microalgae biorefinery with the prime objective of carotenoid production for the nutraceutical and cosmetics sectors (Silva et al. 2020). Cellana (www.cellana.com) organization situated in the USA, is involved in producing biofuel, PUFA, and animal feed from microalgae biomass.

The market value of microalgal research and industry today is indicated by patent activity which determines innovation and development. Several patents have been filed by various companies on algae -based valuable products such as food supplements and high-value proteins. An extensive bibliometric analysis of filed patents was done using Espacenet and Orbit databases representing technological trends in the field of microalgal bioremediation and biorefinery (Pessoa et al. 2021). Table 5 includes distinct technology transfer by the industries and companies on microalgae biorefinery oriented products. A technology was patented by Jiaxing Zeyuan Biolog Products Co. Ltd that provides an important solution in large-scale production of astaxanthin from microalgae. Another patent was filed by Parry Nutraceuticals omega-3 fatty acid production using microalgae. In addition, Carbion Biotech Inc. invented technology for microalgae-based flour production (www.worldwide.espacenet.com). The flour was made by culturing microalgal cells of a Chlorella protothecoides strain at favourable pH and dissolved oxygen conditions to yield a desired amount of lipid. The newest market is expected to grow at a compound annual growth rate (CAGR) of 10.3%, reaching $1.8 billion during the period 2021–2028 mainly in nutraceuticals, animal feed, cosmetics, food and beverages (Bhattacharya and Goswami 2020).

Table 5.

Technology transfer analysis on microalgae biorefinery products (www.worldwide.espacenet.com) (Bhattacharya and Goswami 2020)

Patent number	Publication date	Inventor	Applicants	Title
US2015159179A1	12.12.2013	Manuel RSF, Maria PA, Maite ZC, Javier IA	Abengoa Bioenergia Nuevas Technologias	Methods for producing biofuels and food co-products from using extract of microalgae cultures
US2011303375A1	15.12.2011	Shannon TG, Shi B, Pelky EE, BesawJR, Bernd DW	Kinberly Clark Worldwide Inc	Tissue products containing microalgae material
US2020263125A1	20.08.2020	Kato N	Board of supervisor of Louisiana state University and Agricultural and Mechanical College	Algae-based bioplastics and methods of making
CN105316357A	2.10.2016	Jianhua F, Lei F, Shulan Li, Yuanguang Li, Jun W	Jiaxing Zeyuan Biolog Products Co. Ltd	Methods for producing astaxanthin by using transgenic microalgae
US2012202292A1	05.06.2020	Huang C	–	Novel method to generate bioactive compounds in algae
WO2008013548A2	31.01.2008	Swaminathan K, Sebestian TS	Parry Nutraceuticals	Photoautotrophic growth of microalgae for omega -3 fatty acid production
CN104432093A	25.032015	Nangai H, Guoyou L, Shengfang L	–	Microalgae mulberry heath care buccal tablet and preparation method
US2010297325A1	25.11.2010	Jeff A, Enroque B, Gepffery B, Stephen D, Scott F, LesileN,John P, Walter R, Dana Z	Solazyme	Egg products containing microalgae
US10098371B2	16.10.2018	Norris L, Piechicki J, Baliu E, Desai R, Ruyet ML, Patinier, Passe D, Druon A	Carbion Biotech Inc	Microalgae flour
CN102423021A	25.04.2012	Li J, Huang W, Zheng, Zhang Y	Guangdong Runke Biolog Engineering Co Ltd	Nutrient jelly containing microalgae DHA and preparation method

Biofuel policies, implementations and blending targets

The sustainable commercialization of renewable energy sources like biofuel and bioethanol depends on government organization's legal guidelines and transparent policies. At this juncture, the first mandate on biofuel was adopted in 1948, the Indian Power Alcohol Act, 1948 (Act No. 22 of 1948) (Vasistha et al. 2021a, b). The prime focus of the Act was the 'Power Alcohol' industry in India. The mandate was repleaded in 2000 (Indian Power Alcohol Act (replea), 2000) (Moshood et al. 2021). The US Government initiated research support by approving a bill signed by the Senate Committee in August 2012, which states the tax credit of algal fuels. Energy Independence Security Act (EISA) was established to commercialize biofuel production (Saravanan et al. 2020). The biofuels policies were first recognized by Brazil, followed by the US and Europe Union. In Brazil, ethanol was marked as the official fuel by the State of Pernambuco. In 2017, the National Biofuel Policy (Renovabio) was adopted in Brazil to upsurge the production of biofuels (Klein et al. 2019). The Draft Russian Energy Strategy was extended up till 2035 in Russia with the goal of 12% electricity generation from non-carbon sources. The Russian government has set the National Standard GOST P523368-2005 to blend 5% biodiesel with other liquid fuels (Saravanan et al. 2020). In India, the National Policy on Biofuel was implemented in 2008 to govern biofuel commercialization through firms and companies. In 2018, the National Policy Act was revised to achieve 20% ethanol blending in petrol (E20), whereas 5% was biodiesel blending in diesel in 2030 (Lin and Lu 2021). In India, Rajasthan was the first State to adopt the New Biofuel Policy in 2019. In addition, the Ministry of Petroleum and Natural Gas (MoPNG) released the notification for the ethanol blending Programme (EBP) in 2002 (Moshood et al. 2021). The successful implementation and adaptation of policies rely on the State government's stakeholders. Government officials should work on the concerns related to policies; also, the policies should be revised, which can further improve the regulatory framework.

Challenges and way forward

Numerous industries already accept algae potential as an appropriate and sustainable feedstock for a circular bioeconomy (Stark et al. 2022; Sharma et al. 2021). Biofuel and various high-value-added bio-products make algal biorefinery a competent choice for industries. Despite these tremendous potentials of biorefinery, scaling up is inefficient due to some challenges at different stages of biorefinery (Zhang et al. 2021). The inadequate concentration of algal biomass in a fully grown algae culture is a crucial obstacle to the success of the biorefinery approach. Algal biomass quality and biochemical compositions vary due to seasonality complications that influence the whole process's TEA. Open cultivation systems efficiently provide sufficient algae biomass cost-effectively, but contamination is a significant concern due to which photobioreactors are preferred specifically for edible products production (Peter et al. 2022). The harvesting and dewatering process requires intensive energy and economic investment, which reduces the viability of algal biorefinery concepts. Another significant issue associated with harvesting is reduced segregation ability and unsatisfactory quality of algae biomass (Show et al. 2018). The harsh cell destruction process reduces the functionality of various value-added products, and excessive metal coagulants in flocculation can hamper the quality and quantity of ultimate bio-products (Li et al. 2020). High downstream cost with an inadequate amount of biomass leads to inefficient product recovery. Extraction of high-value-added compounds like astaxanthin, lutein, carotene, PUFA, biofuel, and other co-products like protein and carbohydrates can nullify the expense of cultivation and downstream processing (Lupatini et al. 2017; Gilbert-López et al. 2017). Apart from processing hindrance, complicated rules and regulations for innovative edible products formed by discrete governments and regulatory sovereignty hinder algae products distribution (Sodano et al. 2016). These combined challenges reduce the efficiency of algal biorefinery, due to which large-scale algal biorefinery concepts become economically and sustainably nonviable.

Innovative techniques of genetic engineering can enhance the biosynthesis of cellular components. Incorporation or elimination of target genes at the cellular level may elevate the synthesis of specific biomolecules (Zhang et al. 2019). Genetic engineering techniques collaborated with algal biorefinery may enhance the feasibility of algae-mediated biofuel production. In Spirulina sp., hydrogen production gets enhanced by genetically manipulating the hydrogenase enzyme (Li et al. 2021). Besides genetic engineering, metabolic engineering also appears as a novel option for enhancing biofuel yield through manipulating nitrogen flux. Proteins found in algal biomass through engineered nitrogen flux can be transformed into biofuel and make biorefinery cost-effective. Kumar et al. (2020a, b, c) suggested that transformations in media composition and culture conditions directly affect algal biomass yield and value-added products like TAGs. Under pyruvate supplemented culture, C. Zofingiensis results in 28% elevated astaxanthin, like results observed in malic acid and citrate (Yu et al. 2015). Incorporating ionic solvents instead of organic solvents in lipid extraction may result in higher yield without biomass drying, supporting a cost-effective biorefinery. Hence, incorporating innovative techniques and advanced approaches with a close loop bioeconomy leads to the revolutionarily efficient and sustainable algal biorefinery.

Conclusion

With an ever-escalating globalization and energy consumption, the sustainable biorefinery model is imperative to highlight energy security and climate change. Integrating algal technologies is considered a source of biofuel production and multiple value-added co-products as a biorefinery feedstock. The researchers focus on the biorefinery approach to extricate components encapsulated in microalgae, overcoming significant challenges. Nevertheless, industrial microalgae application faces energy and cost challenges. This review discussed the detailed co-products from algae biomass. The LCA and TEA studies were analysed with rigorous market perusal, upgraded retrieval outcomes, and sustainability index. Current research suggests that the commercialization of biodiesel can attain reduced production costs and increased energy return on investment (EROI) by an integrated algal biorefinery oriented fractionation approach. The simultaneous production of algal biodiesel with value-added co-products in an integrated biorefinery strategy leads to a more cost-effective and feasible alternative. This strategy ultimately improves energy efficacy in an environmentally sustainable manner and generates green employment. The government policies and effective implementation should be adopted for regulating the legal hurdles in the energy market.

Future perspective

Global interest in algal biorefinery is rising, particularly for biofuel and value-added products. Bio-based industrialization is attaining enormous consideration due to its zero waste management strategy, which is not evident in the production of synthetic products. Specific benchmarks have been established to promote algal biorefinery, such as production cost, appropriate algae strain selection, and process viability. An integrated algal biorefinery is environmentally feasible but require major technical improvement that can be resolved by integrating innovative utilizations of the Internet of things (IoT) technologies in algal biorefinery. IoT includes self-regulating automated algae cultivation, administrating and manipulating cultivation variables, productivity optimization, recognize toxic algal species, screening specific algal species, classify microalgae species along with algal cells sustainability detection. To obtain cost-effective, smart, automatic and eco-friendly technology for microalgae biorefinery approach addition of IoT techniques are urge of future (Tham et al. 2022). Further research is highly recommended on a few aspects, such as modifications in algal species and technological advancements in downstream processing. To attain enhanced desirable products using environmental waste like wastewater and CO₂ for growth has led to economic cultivation due to which production of algal products may become feasible for large-scale industries.

Innovative research and development are desired for algal biorefinery for viable commercialization. Evaluation performed via LCA and TEA help in the identification of bottlenecks in these processes, which will lead to further research and innovation. Additionally, the ecological and monetary aspects must be portrayed while framing the government policies in the future.

Declarations

Conflict of interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.